This invention relates to printers of the typewriter or dot matrix type and, more particularly, to mechanisms for selectively coupling their platen shaft and driving gear to allow printer controlled or manual indexing of the platen.
Printers of the typewriter or dot matrix type conventionally have a platen mounted on a shaft which is in turn rotatably mounted on the printer frame. During normal printing, the platen is advanced line-by-line. This may be printer controlled by a stepping motor, for example. Mechanism is also provided so that the platen may be disconnected from its printer controlled driving mechanism and rotated manually to index it as desired.
Although a wide variety of such mechanisms have been provided by the prior art, for example, as shown in U.S. Patent Nos. 3,880,016 and 4,105,106, they have all proved to be deficient in that they were unduly expensive to manufacture and failed to take advantage of less expensive construction made possible by the use of precision moulded plastic elements.